Force sensor

ABSTRACT

A force sensor includes a first structure, four strain generation parts, and a second structure. The first structure is formed in such a way that a third axis penetrates therethrough. The four strain generation parts are provided along first and second axes on a reference plane formed by the first and second axes. The second structure is connected to the first structure with the strain generation parts interposed therebetween. The strain generation parts each includes a first beam part extending along the first axis or the second axis, and a second beam part extending in a direction orthogonal to the first beam part and connected to the first beam part at an intermediate part. The strain generation parts are formed in such a way that they are line-symmetric with respect to both the first axis and the second axis when projected in a direction of the third axis.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromJapanese patent application No. 2020-111197, filed on Jun. 29, 2020, thedisclosure of which is incorporated herein in its entirety by reference.

BACKGROUND

The present disclosure relates to a force sensor.

A force sensor for detecting a force or a moment when a predeterminedforce is transmitted from one structure to another structure through astrain generation part extended between the two structures is known. Theforce sensor calculates a force in a desired axial direction and amoment about a desired axis by detecting a strain generated in thestrain generation part.

For example, Japanese Unexamined Patent Application Publication No.2013-011567 discloses a torque measurement apparatus including metallicand beam-like strain generation parts extended between a primarystructure and a secondary structure. Further, torque is transmitted fromone structure to another structure through the strain generation parts.The torque measurement apparatus includes thin-film type strain sensorsarranged on a surface perpendicular to a torque central axis of thestrain generation parts that detect an amount of strain in the straingeneration parts, and a signal processing unit that directly calculatestorque based on the amount of strain detected by the thin-film typestrain sensors.

SUMMARY

However, the torque measurement apparatus disclosed in JapaneseUnexamined Patent Application Publication No. 2013-011567 is limited tomeasuring torque around the torque central axis and cannot detect, forexample, other forces and directions in three-axis orthogonalcoordinates. On the other hand, for example, a six-axis force sensor fordetecting a force or a moment in a three-axis orthogonal coordinatesystem has been developed. However, in such a force sensor, it isnecessary to calculate a desired force or a desired moment by inputtingstrain detected by a plurality of strain sensors into a decouplingmatrix and performing complicated calculations.

An object of the present disclosure is to provide a force sensor whichdoes not require a complicated calculation.

An first example aspect of the present disclosure is a force sensor fordetecting at least one of a force in each axial direction and a momentabout each axis of a Cartesian coordinate system including a first axis,a second axis, and a third axis orthogonal to each other. The forcesensor includes a first structure, four strain generation parts, and asecond structure. The first structure is formed in such a way that thethird axis passes therethrough. The four strain generation parts areprovided along the first axis and the second axis on a reference planeformed by the first axis and the second axis. The second structure isconnected to the first structure with the strain generation partsinterposed therebetween. Each of the strain generation parts includes afirst beam part extending along the first axis or the second axis and asecond beam part extending in a direction orthogonal to the first beampart and an intermediate part of the second beam part is also connectedto the first beam part. The strain generation parts are formed in such away that the strain generation parts become line-symmetric with respectto both the first axis and the second axis when the strain generationparts are projected in a direction of the third axis.

With such a configuration, the strain generation parts included in theforce sensor can easily separate the strain in the direction of theapplied force when the force is applied in each axial direction.

The above force sensor may further include a plurality of strain sensorpairs on the reference plane of the strain generation parts. In someembodiments, the plurality of strain sensor pairs are arranged in such away that the strain sensor pairs become line-symmetric with respect toboth the first axis and the second axis when the plurality of strainsensor pairs are projected in a direction perpendicular to the referenceplane. In this way, the force sensor can detect an external forcewithout performing a complicated decoupling calculation.

In the above force sensor, the plurality of strain sensor pairs mayinclude at least one of a first sensor group, a second sensor group, athird sensor group, a fourth sensor group, a fifth sensor group, and asixth sensor group. The first sensor group includes the plurality ofstrain sensor pairs arranged on the second beam part of the straingeneration part extending along the first axis. The second sensor groupincludes the plurality of strain sensor pairs arranged on the secondbeam part of the strain generation part extending along the second axis.The third sensor group includes the plurality of strain sensors arrangedon the first beam part on the first axis or the second axis. The fourthsensor group includes the plurality of strain sensor pairs arranged onthe first beam part on the second axis. The fifth sensor group includesthe plurality of strain sensor pairs arranged on the first beam part onthe first axis. The sixth sensor group includes at least either of theplurality of strain sensor pairs arranged across the first axis in apart where the first beam part is connected to the first structure orthe second structure provided on the first axis or the plurality ofstrain sensor pairs arranged across the second axis in a part where thefirst beam part is connected to the first structure or the secondstructure provided on the second axis.

With such a configuration, the force sensor can suitably detect anexternal force corresponding to each sensor group.

In the above force sensor, the strain generation parts may be formed soas to be four-fold symmetric with respect to the third axis, and theplurality of strain sensor pairs may be arranged so as to be four-foldsymmetric with respect to the third axis. Thus, the force sensor candetect the six-axis force in a balanced manner.

The above force sensor may further include at least one of a first forcedetection circuit, a second force detection circuit, a third forcedetection circuit, a first moment detection circuit, a second momentdetection circuit, and a third moment detection circuit. The first forcedetection circuit includes a bridge circuit and is configured to detecta force in a direction of the first axis, the bridge circuit includingthe plurality of strain sensor pairs included in the first sensor group.The second force detection circuit includes a bridge circuit and isconfigured to detect a force in a direction of the second axis, thebridge circuit including the plurality of strain sensor pairs includedin the second sensor group. The third force detection circuit includes abridge circuit and is configured to detect a force in a direction of thethird axis, the bridge circuit including the plurality of strain sensorpairs included in the third sensor group. The first moment detectioncircuit includes a bridge circuit and is configured to detect a momentabout the first axis, the bridge circuit including the plurality ofstrain sensor pairs included in the fourth sensor group. The secondmoment detection circuit includes a bridge circuit and is configured todetect a moment about the second axis, the bridge circuit including theplurality of strain sensor pairs included in the fifth sensor group. Thethird moment detection circuit includes a bridge circuit and isconfigured to detect a moment about the third axis, the bridge circuitincluding the plurality of strain sensor pairs included in the sixthsensor group.

Thus, the force sensor can separate the external force into each axialforce and detect the external force without performing a complicateddecoupling calculation.

In the above force sensor, the first sensor group may include theplurality of strain sensor pairs on both the second beam part on theside connected to the first beam part and the second beam part connectedto the first structure or the second structure, so that the first sensorgroup includes two bridge circuits. In this way, the force sensor canimprove the reliability of the first sensor group.

In the above force sensor, the second sensor group may include theplurality of strain sensor pairs on both the second beam part on theside connected to the first beam part and the second beam part connectedto the first structure or the second structure, so that the secondsensor group includes two bridge circuits. In this way, the force sensorcan improve the reliability of the second sensor group.

In the above force sensor, the third sensor group may include theplurality of strain sensor pairs on the first beam part on the firstaxis and the second axis, so that the third sensor group includes twobridge circuits. In this way, the force sensor can improve thereliability of the third sensor group.

In the above force sensor, the sixth sensor group may include theplurality of strain sensor pairs on both the first beam part provided onthe first axis and the first beam part provided on the second axis, sothat the six sensor group includes two bridge circuits. In this way, theforce sensor can improve the reliability of the sixth sensor group.

In the above force sensor, the first beam part may extend from the firststructure along the first axis or the second axis. In this way, theflexibility in designing the first structure is improved. Further, inthe above force sensor, the first beam part may extend from the secondstructure along the first axis or the second axis. In this way, theflexibility in designing the second structure is improved.

According to the present disclosure, it is possible to provide a forcesensor which does not require a complicated calculation.

The above and other objects, features and advantages of the presentdisclosure will become more fully understood from the detaileddescription given hereinbelow and the accompanying drawings which aregiven by way of illustration only, and thus are not to be considered aslimiting the present disclosure.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a force sensor according to anembodiment;

FIG. 2 is a front view of structures of and strain generation parts ofthe force sensor;

FIG. 3 is a front view of an arrangement of strain sensors in the forcesensor;

FIG. 4 is a circuit diagram of bridge circuits included in a firstsensor group;

FIG. 5 is a circuit diagram of bridge circuits included in a secondsensor group;

FIG. 6 is a circuit diagram of bridge circuits included in a thirdsensor group;

FIG. 7 is a circuit diagram of bridge circuits included in a fourthsensor group;

FIG. 8 is a circuit diagram of bridge circuits included in a fifthsensor group;

FIG. 9 is a circuit diagram of bridge circuits included in a sixthsensor group; and

FIG. 10 is a front view showing an example of a variation of the straingeneration part.

DESCRIPTION OF EMBODIMENTS

Hereinafter, the present disclosure will be described through anembodiment of the disclosure, but the disclosure according to the claimsis not limited to the following embodiment. For clarity of illustration,the following description and drawings have been omitted and simplifiedas appropriate. In the drawings, the same elements are denoted by thesame reference signs, and repeated description is omitted as necessary.

Embodiment

A force sensor according to an embodiment detects a force or a momenttransmitted between two structures by being interposed between the twostructures. The force sensor can be used, for example, in joints such asthe wrist and ankle of a robot, power steering of an automobile, a powertransmission part from a driving motor of a moving apparatus to a wheelinstalled on a moving surface, or a joystick part of a predeterminedcontroller.

An embodiment of the present disclosure will be described below withreference to the drawings. FIG. 1 is a perspective view of a forcesensor 10 according to the embodiment. For convenience of explaining thepositional relationship of the components, FIG. 1 shows a right-handedCartesian coordinate system. In FIG. 2 and the subsequent drawings, whena Cartesian coordinate system is shown, the X-axis, Y-axis, and Z-axisdirections of FIG. 1 correspond to the X-axis, Y-axis, and Z-axisdirections, respectively, of the Cartesian coordinate system in FIG. 2and the subsequent drawings. In this embodiment, the X-axis may bereferred to as a first axis, the Y-axis may be referred to as a secondaxis, and the Z-axis may be referred to as a third axis.

The force sensor 10 detects a force in each axis direction and a momentabout each axis of the Cartesian coordinate system including the X-axis(the first axis), the Y-axis (the second axis), and the Z-axis (thethird axis) that are orthogonal to each other. An entire outer form ofthe force sensor 10 is a substantially rectangular parallelepiped. Inthe substantially rectangular parallelepiped force sensor 10, a planeparallel to the XY plane and on the positive side of the Z-axis is areference plane F10 which has been smoothed. FIG. 1 is a perspectiveview of the force sensor 10 observed from the reference plane F10 side.As shown in the drawing, the reference plane F10 corresponds to the XYplane of the Cartesian coordinate system. The origin of the Cartesiancoordinate system corresponds to the center of the reference plane F10.

The force sensor 10 includes first structures 11, a second structure 12and strain generation parts 13 as main components. The first structures11, the second structure 12, and the strain generation parts 13 areformed by cutting one metal member (e.g., stainless steel or aluminumalloy).

The first structure 11 is a hollow cylindrical structure formed aroundthe Z-axis. The first structure 11 includes a reference hole 110, afirst positioning hole 111, and a first screw hole 112 opened parallelto the Z-axis. The reference hole 110 is a round hole provided at thecenter of the first structure 11, and the central axis of the referencehole 110 corresponds to the Z-axis. The first positioning holes 111 areprovided at four respective positions equidistant from each other in aradial direction around the Z-axis as the central axis and at equalintervals in a circumferential direction around the Z-axis as thecentral axis. The first screw hole 112 is provided on an outerperipheral side of the first positioning holes 111 (the side separatingfrom the Z-axis) corresponding to each of the first positioning holes111 at the four positions. The first structures 11 are connected to thestrain generation parts 13 extending radially along the reference planeF10 around the Z-axis on the X-axis positive side, the X-axis negativeside, the Y-axis positive side, and the Y-axis negative side,respectively.

The second structure 12 is connected to the first structures 11 with thestrain generation parts 13 interposed therebetween. The second structure12 is formed around the Z-axis so as to surround the first structures11. The second structure 12 includes second positioning holes 120 andsecond screw holes 121. The second positioning holes 120 are providednear four respective corners of a contour of a rectangle equidistantfrom each other in a radial direction around the Z-axis as the centralaxis and at equal intervals in a circumferential direction around theZ-axis as the central axis. The second screw holes 121 are provided onan outer peripheral side of the second positioning holes 120corresponding to the respective second positioning holes 120 at the fourpositions. The second structure 12 is connected to the four straingeneration parts 11 extending from the first structures 13 on the X-axisand the Y-axis, respectively.

The strain generation parts 13 are beam-like parts radially extendingfrom the first structures 11 along the X-axis and the Y-axis on thereference plane F10. The force sensor 10 includes four strain generationparts 13. The four strain generation parts 13 included in the forcesensor 10 connect the first structures 11 to the second structure 12 onthe X-axis positive side, the X-axis negative side, the Y-axis positiveside and the Y-axis negative side, respectively.

The force sensor 10 further includes, on the reference plane F10, strainsensors 14, wiring parts 15, and electrodes 16. The plurality of strainsensors 14 are arranged on the reference plane F10 in the straingeneration part 13. The strain sensor 14 is configured in such a waythat it indicates a predetermined resistance value when a voltage isapplied thereto and changes the resistance value when strain isdetected. For example, the strain sensor 14 is configured such that theresistance value increases when it is stretched, and the resistancevalue decreases when it is contracted.

The strain sensor 14 is configured such that an electric signalgenerated by each strain sensor is transmitted to the electrode 16through the wiring part 15. The wiring part 15 connects the strainsensor 14 to the electrode 16 so that the signal generated by the strainsensor 14 is transmitted to the electrode 16. The electrode 16 is aninterface for transmitting and receiving the electric signal. Theelectrode 16 is connected to the strain sensor 14 with the wiring part15 interposed therebetween, and supplies the signal generated by thestrain sensor 14 to the outside.

The strain sensors 14, the wiring parts 15, and the electrodes 16 can beprovided on the reference plane F10 by, for example, the followingsteps. First, an insulating coat is formed by sputtering on a stainlesssteel base material constituting the first structures 11, the secondstructure 12, and the strain generation parts 13. The insulating coatis, for example, silicon dioxide (SiO₂). Next, a film of, for example,chromium nitride (Cr—N) is formed by sputtering as conductive parts ofthe strain sensors 14, the wiring parts 15, and the electrodes 16 on theformed insulating coat. Next, gold (Au) is formed on the partscorresponding to the wiring parts 15 and the electrodes 16 bysputtering. Further, silicon dioxide (SiO₂) is formed as a protectivefilm on the parts corresponding to the strain sensors 14 and the wiringparts 15. By manufacturing the strain sensors 14, the wiring parts 15,and the electrodes 16 by such a method, it is possible to realize adesired configuration of the force sensor 10 in a space-saving manner.The above-described manufacturing method is already known to a personskilled in the art, and a detailed description of the maskingprocessing, etc. is omitted here.

The strain sensors 14, the wiring parts 15, and the electrodes 16 can beformed not only by the above described steps but also by other methods.For example, the wiring parts 15 and the electrodes 16 can be connectedto a conductive member using wire bonding, soldering, or the like. Thestrain sensors 14 may also be implemented by connecting semiconductorstrain gauges or other common strain gauges. The insulating coat and theprotective film may be formed by coating or dipping instead of thesputtering step described above.

In the following description, when an external force is applied to theforce sensor 10, it is assumed that the first structure 11 is a forcereceiving part, and the external force received by the first structure11 is transmitted to the second structure 12 through the straingeneration part 13. The first structure 11 may be referred to as astructure on a primary side or an input side, and the second structure12 may be referred to as a structure on a secondary side or an outputside.

Next, the shape of the strain generation part 13 will be described withreference to FIG. 2 . FIG. 2 is a front view showing the structures andthe strain generation parts of the force sensor. FIG. 2 schematicallyshows the force sensor 10 with some of components omitted as appropriatein order to explain the shape of the strain generation part 13.

The first structures 11 are connected to the second structure 12 by thefour strain generation parts 13. The strain generation parts 13 extend(radially) toward the second structure 12 along the respective axes fromfour positions on the X-axis positive side, the X-axis negative side,the Y-axis positive side, and the Y-axis negative side of the firststructure 11, respectively, and branch into two along thecircumferential direction around the Z-axis, and then the branched partsare connected to the second structure 12.

In the following description, among the four strain generation parts 13,the one positioned on the X-axis positive side is referred to as astrain generation part 13A, the one positioned on the Y-axis negativeside is referred to as a strain generation part 13B, the one positionedon the X-axis negative side is referred to as a strain generation part13C, and the one positioned on the Y-axis positive side is referred toas a strain generation part 13D. In the following description, thestrain generation parts 13A to 13D may be collectively referred to asthe strain generation parts 13.

Each of the strain generation parts 13 includes a connection part 135, afirst beam part 136, and a second beam part 137. The connection part 135is a part connected to the first structure 11. The connection part 135is positioned on the X-axis or the Y-axis. The first beam part 136 is abeam-like part extending from the connection part 135 toward the secondstructure 12. The second beam part 137 is a beam-like part extending ina direction orthogonal to the first beam part 136, and an intermediatepart of the second beam part 137 is connected to the first beam part136. One end side of the first beam part 136 is connected to theintermediate part of the second beam part 137, so that the straingeneration part 13 is formed in a T-shape.

The force sensor 10 is formed so that, when projected in a directionperpendicular to the reference plane F10 (XY Plane), i.e., in the Z-axisdirection, the strain generation parts 13 become line-symmetric witheach other with respect to both the X-axis and the Y-axis. For example,the strain generation part 13A and the strain generation part 13C areline-symmetric with respect to the Y-axis, and the strain generationpart 13A and the strain generation part 13C are also line-symmetric withrespect to the X-axis.

The strain generation parts 13 according to this embodiment are formedfour-fold symmetric with respect to the Z-axis. That is, the straingeneration parts 13 are formed in such a way that the shapes of thestrain generation parts 13 after the force sensor 10 is rotated by 90degrees around the Z-axis become the same as the shapes of the straingeneration parts 13 before the force sensor 10 is rotated by 90 degrees.For example, the shape of the strain generation part 13A projected ontothe XY plane is the same as the shape of the strain generation part 13Bwhen the force sensor 10 is rotated clockwise by 90 degrees around theZ-axis.

With the above-described shape of the force sensor 10, when a force ineach axial direction and a moment about each axis, which are externalforces, are applied, the force sensor generates in-plane strain andout-of-plane strain as shown below.

The in-plane strain is strain in the strain generation part generated inthe reference plane F10 when the external force is applied to the forcesensor 10. The in-plane strain is caused by a force Fx in the X-axisdirection, a force Fy in the Y-axis direction, and a moment Mz about theZ-axis. When Fx is applied to the force sensor 10, the strain issuitably generated in the strain generation part 13A to the straingeneration part 13D, and the first structure 11 is displaced parallel tothe X-axis. When the force Fy is applied to the force sensor 10, thestrain is suitably generated in the strain generation part 13A to thestrain generation part 13D, and the first structure 11 is displacedparallel to the Y-axis. When the moment Mz is applied to the forcesensor 10, the strain is uniformly generated in each of the straingeneration parts 13A to 13D, and the first structure 11 is rotatedaround the Z-axis.

The out-of-plane strain is strain in the strain generation partgenerated outside the reference plane F10 when the external force isapplied to the force sensor 10. The out-of-plane strain is caused by aforce Fz in the Z-axis direction, a moment Mx about the X-axis, and amoment My about the Y-axis. When Fz is applied to the force sensor 10,the strain is uniformly generated in each of the strain generation parts13A to 13D, and the first structure 11 is displaced parallel to theZ-axis. When Mx is applied to the force sensor 10, the strain issuitably generated in the strain generation parts 13A to 13D, and thefirst structure 11 rotates about the X-axis. When the moment My isapplied to the force sensor 10, the strain is suitably generated in thestrain generation parts 13A to 13D, and the first structure 11 rotatesaround the Y-axis.

As described above, since the shapes of the strain generation parts 13have symmetry, the amounts of strain in the strain generation parts 13have symmetry when the external force is applied. Thus, the force sensor10 can arrange the strain sensors so as to detect the external forcewithout performing a complicated decoupling calculation.

Note that the second beam part 137 needs not be extended along thecircumferential direction around the Z-axis and instead may be linearlyextended or curved, or the widths and thickness of the second beam part137 may vary. Further, the connection part 135 and the first beam part136 are gradually changed and are not clearly defined, and the boundarypart between them may belong to either the connection part 135 or thefirst beam part 136. The same is applied to the boundary between thefirst beam part 136 and the second beam part 137. The boundary betweenthe first structures 11 and the strain generation parts 13 and theboundary between the strain generation part 13 and the second structureare also gradually changed and are not clearly defined.

Next, the arrangement of the strain sensors 14 will be described withreference to FIG. 3 . FIG. 3 is a front view showing the arrangement ofthe strain sensors in the force sensor 10.

Each of the strain generation parts 13A to 13D includes ten strainsensors 14. The ten strain sensors 14 included in each of the straingeneration parts 13A to 13D are arranged at positions at which thestrain generation parts 13A to 13D are relatively four-fold symmetricwith respect to the Z-axis. As a representative example, the arrangementof the strain sensors 14 included in the strain generation part 13A willbe described below.

The strain generation part 13A includes ten strain sensors 14 defined assensors A01 to A10. The sensor A01 is provided on the X-axis in theconnection part 135. The sensor A02 is provided on the X-axis in thepart where the first beam part 136 is connected to the second beam part137. The sensor A03 is provided at a position where it does not overlapthe sensor A01 on the X-axis in the connection part 135. The sensor A04is provided at a position where it does not overlap the sensor A02 onthe X-axis in the part where the first beam part 136 is connected to thesecond beam part 137. The sensor A05 and the sensor A06 are provided atpositions symmetric with respect to the X-axis across the X-axis in theconnection part 135. The sensor A07 and the sensor A08 are provided atpositions symmetric with respect to the X-axis across the X-axis in thesecond beam part 137 on the side close to the first beam part 136. Thesensor A09 and the sensor A10 are provided at positions symmetric withrespect to the X-axis across the X-axis in the second beam part 137 onthe side close to the connection part connected to the second structure12.

Commonly, the amount of strain when a cantilever beam is bent by anexternal force increases as the distance from the neutral planeincreases. For this reason, the sensors A07 to A10 are positioned farfrom a neutral plane when the in-plane strain is generated in the straingeneration parts 13. By doing so, the force sensor 10 can detect thein-plane strain with high sensitivity.

Like the above-described strain generation part 13A, the straingeneration parts 13B, 13C, and 13D each include ten strain sensors 14.As shown in FIG. 3 , each of the sensors included in each of the straingeneration parts is labeled with a combination of an alphabet and anumeral, where the alphabets A to D correspond to the strain generationparts 13A to 13D, respectively, and numerals 01 to 10 correspond to thearrangement of the sensors.

As described above, the force sensor 10 according to the embodiment hassuch a structure that the configuration of the first structure can besimplified. Thus, the force sensor 10 according to the embodiment canimprove the flexibility in designing the first structure.

Next, a strain sensor pair and a sensor group will be described withreference to FIGS. 4 to 9 . Each of the strain sensors 14 of the forcesensor 10 constitutes the strain sensor pair. Each strain sensor pair isan element for constituting one bridge circuit. The sensor groupincludes a plurality of the strain sensor pairs, and one sensor groupincludes the bridge circuits for detecting a corresponding axial forceor a corresponding axial moment. The force sensor 10 includes a firstsensor group SG1 to a sixth sensor group SG6.

In the bridge circuit according to this embodiment, an input voltage Viis applied to one end of a parallel circuit, which is composed of twostrain sensors connected in parallel, and the other end of the parallelcircuit is grounded. An output voltage Vo of an intermediate part of theparallel circuit is output. When the strain sensors constituting thebridge circuit expand/contract due to the strain in the straingeneration part 13, the resistance value of the expanded/contractedstrain sensor 14 changes. Thus, when the strain sensor 14 detectsstrain, a value of the output voltage Vo changes accordingly.

FIG. 4 is a circuit diagram of the first sensor group SG1. The forcesensor 10 includes the first sensor group SG1 for detecting the forceFx. In the illustrated circuit diagram, each resistor represents thestrain sensor 14. The first sensor group SG1 includes a bridge circuitBFx1 and a bridge circuit BFx2.

The bridge circuit BFx1 includes the sensors A07, A08, C07, and C08 asfour strain sensors 14. The sensor A07 and the sensor A08 are arrangedat positions symmetric with respect to the X-axis, and constitute onestrain sensor pair. Likewise, the sensor C07 and the sensor C08 arearranged at positions symmetric with respect to the X-axis, andconstitute one strain sensor pair.

The bridge circuit BFx2 includes the sensors A09, A10, C09, and C10. Thesensor A09 and the sensor A10 are arranged at positions symmetric withrespect to the X-axis, and constitute one strain sensor pair. Likewise,the sensor C09 and the sensor C10 are arranged at positions symmetricwith respect to the X-axis, and constitute one strain sensor pair.

The first sensor group SG1 detects the force Fx in accordance with thefollowing Formula (1).[Equation 1]Fx=((RA07+RA08)−(RC07+RC08))+((RA09+RA10)−(RC09+RC10))  (1)

Each term on the right side of Formula (1) represents a change in theresistance value of each sensor. For example, when the resistance valueof the sensor A07 is increased due to the strain in the straingeneration part 13, “(+)” is applied to the RA07. Alternatively, whenthe resistance value of the sensor A07 decreases, “(−)” is applied tothe RA07. When there is no change in the resistance value of the sensorA07, “(0)” is applied. The same applies to the following force or momentequations.

Next, an output of the first sensor group SG1 when a predeterminedexternal force is applied to the force sensor 10 will be described. Thefirst sensor group SG1 is represented as follows when a force in eachaxial direction and a moment about each axis are applied.Fx+=(((+)+(+))−((−)+(−)))+(((+)+(+))−((−)+(−)))=8(+)Fy+=(((+)+(−))−((−)+(+)))+(((+)+(−))−((−)+(+)))=0Fz+=(((0)+(0))−((0)+(0)))+(((0)+(0))−((0)+(0)))=0Mx+=(((−)+(+))−((+)+(−)))+(((−)+(+))−((+)+(−)))=0My+=(((0)+(0))−((0)+(0)))+(((0)+(0))−((0)+(0)))=0Mz+=(((+)+(−))−((+)+(−)))+(((−)+(+))−((−)+(+)))=0  [Equation 2]

In this formula Fx+ is a force in the X-axis positive direction, Fy+ isa force in the Y-axis positive direction, Fz+ is a force in the Z-axispositive direction, Mx+ is a moment about the X-axis in the positivedirection, My+ is the moment about the Y-axis in the positive direction,and Mz+ is the moment about the Z-axis in the positive direction. Inthis embodiment, the positive direction of the moment is a direction ofclockwise rotation when the positive side of the corresponding axis isviewed from the negative side.

As shown above, the first sensor group SG1 becomes 8 (+) when the forceFx+ in the X-axis positive direction is applied. Thus, the Fx detectioncircuit detects Fx with high sensitivity. On the other hand, forexample, when an external force Fy+ in the Y-axis direction is appliedto the first sensor group SG1, the change in the resistance values ofthe strain sensors 14 of the sensor group becomes (+) or (−) due to theexpansion and contraction of the corresponding sensor, but consequentlybecomes zero, because the expansion and contraction of the respectivesensors have symmetry. When the force Fz+ in the Z-axis direction isapplied, no strain is generated (the strain sensors are insensible tothe force Fz+), so that all terms become (0). Thus, when an externalforce in directions other than the Z-axis direction is applied, thechange in the resistance value of the strain sensor 14 of the sensorgroup becomes zero as a result. In other words, the output of the firstsensor group SG1 is in equilibrium with the external force that is notthe force Fx.

FIG. 5 is a circuit diagram of the second sensor group SG2. The forcesensor 10 includes the second sensor group SG2 for detecting the forceFy. The second sensor group SG2 includes a bridge circuit BFy1 and abridge circuit BFy2.

The bridge circuit BFy1 includes the sensors the D07, D08, B07, and B08.The sensor D07 and the sensor D08 are arranged at positions symmetricwith respect to the Y-axis, and constitute one strain sensor pair.Likewise, the sensor B07 and the sensor B08 are arranged at positionssymmetric with respect to the Y-axis, and constitute one strain sensorpair.

The sensors D09 and D10 are arranged at positions symmetric with respectto the Y-axis, and constitute one strain sensor pair. Likewise, thesensor B09 and the sensor B10 are arranged at positions symmetric withrespect to the Y-axis, and constitute one strain sensor pair.

The second sensor group SG2 detects the force Fy in accordance with thefollowing Formula (2).

[Equation 3]Fy=((RD07+RD08)−(RB07+RB08))+((RD09+RD10)−(RB09+RB10))  (2)

Next, an output of the second sensor group SG2 when a predeterminedexternal force is applied to the force sensor 10 will be described. Thesecond sensor group SG2 is represented as follows when a force in eachaxial direction and a moment about each axis are applied.Fx+=(((+)+(−))−((−)+(+)))+(((+)+(−))−((−)+(+)))=0Fy+=(((+)+(+))−((−)+(−)))+(((+)+(+))−((−)+(−)))=8(+)Fz+=(((0)+(0))−((0)+(0)))+(((0)+(0))−((0)+(0)))=0Mx+=(((0)+(0))−((0)+(0)))+(((0)+(0))−((0)+(0)))=0My+=(((−)+(−))−((+)+(+)))+(((+)+(+))−((−)+(−)))=0Mz+=(((+)+(−))−((+)+(−)))+(((−)+(+))−((−)+(+)))=0  [Equation 4]

As shown above, the second sensor group SG2 becomes 8 (+) when the forceFy+ in the Y-axis positive direction is applied. Thus, the Fy detectioncircuit detects Fy with high sensitivity. On the other hand, when anexternal force in a direction other than the Y-axis positive directionis applied to the second sensor group SG2, the change in the resistancevalues of the strain sensors 14 of the sensor group consequently becomeszero due to the expansion and contraction of the respective strainsensors, because the expansion and contraction of the respective sensorshave symmetry or becomes zero, because the strain sensors are insensibleto the external force in the direction other than the Y-axis positivedirection.

FIG. 6 is a circuit diagram of the third sensor group SG3. The forcesensor 10 includes the third sensor group SG3 for detecting the forceFz. The third sensor group SG3 includes a bridge circuit BFz1 and abridge circuit BFz2.

The bridge circuit BFz1 includes the sensors A01, C01, A02, and C02. Thesensors A01 and C01 are arranged at positions symmetric with respect tothe Y-axis, and constitute one strain sensor pair. Likewise, the sensorA02 and the sensor C02 are arranged at positions symmetric with respectto the Y-axis, and constitute one strain sensor pair.

The bridge circuit BFz2 includes the sensors B01, D01, B02, and D02. Thesensor B01 and the sensor D01 are arranged at positions symmetric withrespect to the X-axis, and constitute one strain sensor pair. Likewise,the sensor B02 and the sensor D02 are arranged at positions symmetricwith respect to the X-axis, and constitute one strain sensor pair.

The third sensor group SG3 detects the force Fz in accordance with thefollowing Formula (3).[Equation 5]Fz=(RA01+RC01)−(RA02+RC02))+((RB01+RD01)−(RB02+RD02))  (3)

Next, an output of the third sensor group SG3 when a predeterminedexternal force is applied to the force sensor 10 will be described. Thethird sensor group SG3 is represented as follows when a force in eachaxial direction and a moment about each axis are applied.Fx+=(((0)+(0))−((0)+(0)))+(((0)+(0))−((0)+(0)))=0Fy+=(((0)+(0))−((0)+(0)))+(((0)+(0))−((0)+(0)))=0Fz+=(((+)+(+))−((−)+(−)))+(((+)+(+))−((−)+(−)))=8(+)Mx+=(((0)+(0))−((0)+(0)))+(((−)+(+))−((+)+(−)))=0My+=(((−)+(+))−((+)+(−)))+(((0)+(0))−((0)+(0)))=0Mz+=(((0)+(0))−((0)+(0)))+(((0)+(0))−((0)+(0)))=0  [Equation 6]

As shown above, the third sensor group SG3 becomes 8 (+) when the forceFz+ in the Z-axis positive direction is applied. Thus, the Fz detectioncircuit detects Fz with high sensitivity. On the other hand, when anexternal force in a direction other than the Z-axis positive directionis applied to the third sensor group SG3, the resistance values of thestrain sensors 14 do not change (the change is 0) in most cases. WhenMx+ and My+ are applied, the change in the resistance values of thestrain sensors 14 of the sensor group becomes (+) or (−) due to theexpansion and contraction of some of the strain sensors 14. However, theoutput of the third sensor group SG3 consequently becomes zero, becausethe expansion and contraction of the respective sensors have symmetry.

FIG. 7 is a circuit diagram of the fourth sensor group SG4. The forcesensor 10 includes the fourth sensor group SG4 for detecting a momentMx. The fourth sensor group SG4 includes a bridge circuit BMx1.

The bridge circuit BMx1 includes the sensors B03, D03, B04, and D04. Thesensors B03 and the sensor D03 are arranged at positions symmetric withrespect to the X-axis, and constitute one strain sensor pair. The sensorB04 and the sensor D04 are arranged at positions symmetric with respectto the X-axis, and constitute one strain sensor pair.

The fourth sensor group SG4 detects the moment Mx in accordance with thefollowing Formula (4).[Equation 7]Mx=(RD03−RB03)+RB04−RD04)  (4)

Next, an output of the fourth sensor group SG4 when a predeterminedexternal force is applied to the force sensor 10 will be described. Thefourth sensor group SG4 is represented as follows when a force in eachaxial direction and a moment about each axis are applied.Fx+=(((0)−(0))+((0)−(0)))=0Fy+=(((0)−(0))+((0)−(0)))=0Fz+=(((+)−(+))+((−)−(−)))=0Mx+=(((+)−(−))+((+)−(−)))=4(+)My+=(((0)−(0))+((0)−(0)))=0Mz+=(((0)−(0))+((0)−(0)))=0  [Equation 8]

Thus, the fourth sensor group SG4 becomes 4 (+) when the moment Mx+about the X-axis positive direction is applied. Thus, the Mx detectioncircuit detects Mx with high sensitivity. On the other hand, when anexternal force in a direction other than the X-axis positive directionis applied to the fourth sensor group SG4, the resistance values of thestrain sensors 14 do not change (the change is 0) in most cases. WhenFz+ is applied, the change in the resistance values of the strainsensors 14 of the sensor group becomes (+) or (−) due to the expansionand contraction of some of the strain sensors 14. However, the output ofthe fourth sensor group SG4 consequently becomes zero, because theexpansion and contraction of the respective sensors have symmetry.

FIG. 8 is a circuit diagram of the fifth sensor group SG5. The forcesensor 10 includes the fifth sensor group SG5 for detecting a moment My.The fifth sensor group SG5 includes a bridge circuit BMy1.

The bridge circuit BMy1 includes the sensors A03, C03, A04, and C04. Thesensor A03 and the sensor C03 are arranged at positions symmetric withrespect to the Y-axis, and constitute one strain sensor pair. The sensorA04 and the sensor C04 are arranged at positions symmetric with respectto the Y-axis, and constitute one strain sensor pair.

The fifth sensor group SG5 detects the moment My in accordance with thefollowing Formula (5).[Equation 9]My=(RC03−RA03)+(RA04−RC04)  (5)

Next, an output of the fifth sensor group SG5 when a predeterminedexternal force is applied to the force sensor 10 will be described. Thefifth sensor group SG5 is represented as follows when a force in eachaxial direction and a moment about each axis are applied.Fx+=(((0)−(0))+((0)−(0)))=0Fy+=(((0)−(0))+((0)−(0)))=0Fz+=(((+)−(+))+((−)−(−)))=0Mx+=(((0)−(0))+((0)−(0)))=0My+=(((+)−(−))+((+)−(−)))=4(+)Mz+=(((0)−(0))+((0)−(0)))=0  [Equation 10]

Thus, the fifth sensor group SG5 becomes 4 (+) when the moment My+ aboutthe Y-axis positive direction is applied. Thus, the My detection circuitdetects My with high sensitivity. On the other hand, when an externalforce in a direction other than the Y-axis positive direction is appliedto the fifth sensor group SG5, the resistance values of the strainsensors 14 do not change (the change is 0) in most cases. When Fz+ isapplied, the change in the resistance values of the strain sensors 14 ofthe sensor group becomes (+) or (−) due to the expansion and contractionof some of the strain sensors 14. However, the output of the fifthsensor group SG5 consequently becomes zero, because the expansion andcontraction of the respective sensors have symmetry.

FIG. 9 is a circuit diagram of the sixth sensor group SG6. The forcesensor 10 includes the sixth sensor group SG6 for detecting a moment Mz.The sixth sensor group SG6 includes a bridge circuit BMz1 and a bridgecircuit BMz2.

The bridge circuit BMz1 includes the sensors A05, C06, C05, and A06.

The sensor A05 and the sensor C06 are arranged at positions symmetricwith respect to the Y-axis, and constitute one strain sensor pair.Likewise, the sensor C05 and the sensor A06 are arranged at positionssymmetric with respect to the Y-axis, and constitute one strain sensorpair.

The bridge circuit BMz2 includes the sensors B05, D06, D05, and B06. Thesensor B05 and the sensor D06 are arranged at positions symmetric withrespect to the X-axis, and constitute one strain sensor pair. Likewise,the sensor D05 and the sensor B06 are arranged at positions symmetricwith respect to the X-axis, and constitute one strain sensor pair.

The sixth sensor group SG6 detects the moment Mz in accordance with thefollowing Formula (6).[Equation 11]Mz=((RA05+RC05)−(RA06+RC06))+((RB05+RD05)−(RB06+RD06)  (6)

Next, an output of the sixth sensor group SG6 when a predeterminedexternal force is applied to the force sensor 10 will be described. Thesixth sensor group SG6 is represented as follows when a force in eachaxial direction and a moment about each axis are applied.Fx+=(((−)+(+))−((−)+(+)))+(((+)+(−))−((−)+(+)))=0Fy+=(((+)+(−))−((−)+(+)))+(((+)+(−))−((+)+(−)))=0Fz+=(((+)+(+))−((+)+(+)))+(((+)+(+))−((+)+(+)))=0Mx+=(((+)+(−))−((−)+(+)))+(((−)+(+))−((−)+(+)))=0My+=(((−)+(+))−((−)+(+)))+(((−)+(+))−((+)+(−)))=0Mz+=(((+)+(+))−((−)+(−)))+(((+)+(+))−((−)+(−)))=8(+)  [Equation 12]

As shown above, the sixth sensor group SG6 becomes 8 (+) when the momentMz+ about the Z-axis positive direction is applied. Thus, the Mzdetection circuit detects Mz with high sensitivity. On the other hand,when an external force in a direction other than the Z-axis positivedirection is applied to the sixth sensor group SG6, the output of thesixth sensor group SG6 becomes (+) or (−) due to the expansion andcontraction of the corresponding strain sensor 14, but consequentlybecomes zero, because the expansion and contraction of the respectivesensors have symmetry.

As described above, the force sensor 10 is arranged in such a way thatthe shapes of the strain generation parts 13 become symmetric withrespect to the X-axis and the Y-axis, the shapes of the straingeneration parts 13 become four-fold symmetric with respect to theZ-axis, and the strain sensors become symmetric with respect to theX-axis and the Y-axis, and the strain sensors become four-fold symmetricwith respect to the Z-axis. Therefore, when the force sensor 10 detectsthe force in each axial direction and the moment about each axialdirection, the force sensor can detect the external force in eachdirection separately without performing a complicated decouplingcalculation.

Next, a multiplex configuration employed by the force sensor 10according to the embodiment will be described. A force sensor mounted onvarious actuators is expected to have high reliability in some cases.Therefore, the force sensor 10 according to the embodiment uses aplurality of strain sensors when detecting an external force in apredetermined direction.

More specifically, as shown in FIG. 4 , the force sensor 10 uses thebridge circuit BFx1 and the bridge circuit BFx2 when detecting Fx. Inthis way, the force sensor 10 detects outputs from the two bridgecircuits when detecting an external force in one direction. With such aconfiguration, the force sensor 10 prevents or minimizes deteriorationin reliability.

Similarly, by detecting signals from the two bridge circuits in the Fydetection circuit shown in FIG. 5 , the Fz detection circuit shown inFIG. 6 , and the Mz detection circuit shown in FIG. 9 , the force sensor10 according to the embodiment realizes multiplexing of the detectioncircuits.

Although an example is shown in which the moment Mx shown in FIG. 7 andthe moment My shown in FIG. 8 are not multiplexed, the moment Mx and themoment My can be multiplexed. Specifically, for example, when the Mxdetection circuit is multiplexed, one strain sensor pair may be arrangedon the Y-axis of the strain generation part 13B, and another strainsensor pair may be arranged on the Y-axis of the strain generation part13D at positions symmetric with respect to the X-axis.

Although the force sensor 10 according to the embodiment is shown as anexample in which multiplexing using the plurality of bridge circuits isemployed, the force sensor 10 according to the embodiment is not limitedto this and may be configured not to employ multiplexing. In this case,the force sensor 10 may include, for example, the bridge circuit BFx1 inthe first sensor group SG1 and may not include the bridge circuit BFx2.As described above, whether or not the multiplexing is performed, theforce sensor 10 can detect the external force without performing adecoupling calculation by arranging the strain sensor pairs in asymmetric manner with respect to the X-axis and the Y-axis.

Further, although the force sensor 10 is shown as an example of asix-axis force sensor, the force sensor 10 may detect one or moreexternal forces from among forces along the six axes. For example, ifthe force sensor 10 includes only the first sensor group SG1, it candetect only Fx.

Further, in the force sensor 10 described above, an example is shown inwhich the shape of the strain generation part 13 is four-fold symmetric.Alternatively, the force sensor 10 may be symmetric with respect to theX and Y axes and may not be four-fold symmetric. Similarly, thearrangement of strain sensors 14 may be symmetric with respect to the Xand Y axes and not four-fold symmetric. Specifically, for example, theforce sensor may be elliptical, and the strain generation part extendingon the same axis may be symmetric and not four-fold symmetric.

Modified Example of the Embodiment

Next, a modified example of the embodiment will be described withreference to FIG. 10 . FIG. 10 is a front view showing an example of avariation of the strain generation part. The force sensor 10 shown inFIG. 10 is different from the force sensor described above in that thestrain generation parts 13 are replaced by strain generation parts 23.

In the following description, among the four strain generation parts 23,the one positioned on the X-axis positive side is referred to as astrain generation part 23A, the one positioned on the Y-axis negativeside is referred to as a strain generation part 23B, the one positionedon the X-axis negative side is referred to as a strain generation part23C, and the one positioned on the Y-axis positive side is referred toas a strain generation part 23D. In the following description, thestrain generation parts 23A to 23D may be collectively referred to asthe strain generation parts 23.

The first structures 11 are connected to the second structure 12 by thefour strain generation parts 23. The strain generation parts 23 extendtoward the first structure along the respective axes from four positionson the X-axis positive side, the X-axis negative side, the Y-axispositive side, and the Y-axis negative side of the second structure 12,respectively, and branch into two along the circumferential directionaround the Z-axis, and then the branched parts are connected to thefirst structures 11, respectively.

Each of the strain generation parts 23 includes a connection part 235, afirst beam part 236, and a second beam part 237. The connection part 235is a part connected to the second structure 12. The connection part 235is positioned on the X-axis or the Y-axis. The first beam part 236 is abeam-like part extending from the connection part 235 toward the firststructure 11. The second beam part 237 is a beam-like part extending ina direction orthogonal to the first beam part 236, and an intermediatepart of the second beam part 237 is connected to the first beam part236. One end side of the first beam part 236 is connected to theintermediate part of the second beam part 237, so that the straingeneration part 23 is formed in a T-shape or a Y-shape.

Next, an arrangement of the strain sensors 14 will be explained. As arepresentative example, the arrangement of the ten strain sensors 14included in the strain generation part 23A will be described below.

The strain generation part 23A includes ten strain sensors 14 defined assensors A01 to A10. The sensor A01 is provided on the X-axis in theconnection part 235. The sensor A02 is provided on the X-axis in thepart where the first beam part 236 is connected to the second beam part237. The sensor A03 is provided at a position where it does not overlapthe sensor A01 on the X-axis in the connection part 235. The sensor A04is provided at a position where it does not overlap the sensor A02 onthe X-axis in the part where the first beam part 236 is connected to thesecond beam part 237. The sensor A05 and the sensor A06 are provided atpositions symmetric with respect to the X-axis across the X-axis in theconnection part 235. The sensor A07 and the sensor A08 are provided atpositions symmetric with respect to the X-axis across the X-axis in thesecond beam part 237 on the side close to the first beam part 236. Thesensor A09 and the sensor A10 are provided at positions symmetric withrespect to the X-axis across the X-axis in the second beam part 237 onthe side close to the connection part connected to the first structure11.

Commonly, the amount of strain when a cantilever beam is bent by anexternal force increases as the distance from the neutral planeincreases. For this reason, the sensors A07 to A10 are positioned farfrom a neutral plane when the in-plane strain is generated in the straingeneration parts 13. By doing so, the force sensor 10 can detect thein-plane strain with high sensitivity.

As described above, the force sensor 10 according to the modifiedexample of the embodiment has such a structure that the configuration onthe second structure side can be simplified. Thus, the force sensor 10according to the modified example of the embodiment can improve theflexibility in designing the second structure.

The embodiment has been described above. According to the embodiment, itis possible to provide a force sensor that does not require complicatedcalculations.

Note that the present disclosure is not limited to the above-describedembodiment, and may be modified as appropriate without departing fromthe spirit of the disclosure.

From the disclosure thus described, it will be obvious that theembodiments of the disclosure may be varied in many ways. Suchvariations are not to be regarded as a departure from the spirit andscope of the disclosure, and all such modifications as would be obviousto one skilled in the art are intended for inclusion within the scope ofthe following claims.

What is claimed is:
 1. A force sensor for detecting at least one of aforce in each axial direction and a moment about each axis of aCartesian coordinate system including a first axis, a second axis, and athird axis orthogonal to each other, the force sensor comprising: afirst structure formed in such a way that the third axis passestherethrough; four strain generation parts provided along the first axisand the second axis on a reference plane formed by the first axis andthe second axis; a second structure connected to the first structurewith the strain generation parts interposed therebetween, wherein eachof the strain generation parts comprises a first beam part extendingalong the first axis or the second axis and a second beam part extendingin a direction orthogonal to the first beam part and an intermediatepart of the second beam part is also connected to the first beam part,and the strain generation parts are formed in such a way that the straingeneration parts become line-symmetric with respect to both the firstaxis and the second axis when the strain generation parts are projectedin a direction of the third axis, a plurality of strain sensor pairs onthe reference plane of the strain generation parts, the plurality ofstrain sensor pairs are arranged in such a way that the strain sensorpairs become line-symmetric with respect to both the first axis and thesecond axis when the plurality of strain sensor pairs are projected in adirection of the third axis, and wherein the force sensor furthercomprising at least one of: a first sensor group including the pluralityof strain sensor pairs arranged on the second beam part of the straingeneration part extending along the first axis; a second sensor groupincluding the plurality of strain sensor pairs arranged on the secondbeam part of the strain generation part extending along the second axis;a third sensor group including the plurality of strain sensors arrangedon the first beam part on the first axis or the second axis; a fourthsensor group including the plurality of strain sensor pairs arranged onthe first beam part on the second axis; a fifth sensor group includingthe plurality of strain sensor pairs arranged on the first beam part onthe first axis; and a sixth sensor group including at least either ofthe plurality of strain sensor pairs arranged across the first axis in apart where the first beam part is connected to the first structure orthe second structure provided on the first axis or the plurality ofstrain sensor pairs arranged across the second axis in a part where thefirst beam part is connected to the first structure or the secondstructure provided on the second axis.
 2. The force sensor according toclaim 1, wherein the strain generation parts are formed so as to befour-fold symmetric with respect to the third axis, and the plurality ofstrain sensor pairs are arranged so as to be four-fold symmetric withrespect to the third axis.
 3. The force sensor according to claim 1,further comprising at least one of: a first force detection circuitincluding a bridge circuit and configured to detect a force in adirection of the first axis, the bridge circuit including the pluralityof strain sensor pairs included in the first sensor group; a secondforce detection circuit including a bridge circuit and configured todetect a force in a direction of the second axis, the bridge circuitincluding the plurality of strain sensor pairs included in the secondsensor group; a third force detection circuit including a bridge circuitand configured to detect a force in a direction of the third axis, thebridge circuit including the plurality of strain sensor pairs includedin the third sensor group; a first moment detection circuit including abridge circuit and configured to detect a moment about the first axis,the bridge circuit including the plurality of strain sensor pairsincluded in the fourth sensor group; a second moment detection circuitincluding a bridge circuit and configured to detect a moment about thesecond axis, the bridge circuit including the plurality of strain sensorpairs included in the fifth sensor group; and a third moment detectioncircuit including a bridge circuit and configured to detect a momentabout the third axis, the bridge circuit including the plurality ofstrain sensor pairs included in the sixth sensor group.
 4. The forcesensor according to claim 3, wherein the first sensor group includes theplurality of strain sensor pairs on both the second beam part on theside connected to the first beam part and the second beam part connectedto the first structure or the second structure, so that the first sensorgroup includes two bridge circuits.
 5. The force sensor according toclaim 3, wherein the second sensor group includes the plurality ofstrain sensor pairs on both the second beam part on the side connectedto the first beam part and the second beam part connected to the firststructure or the second structure, so that the second sensor groupincludes two bridge circuits.
 6. The force sensor according to claim 3,wherein the third sensor group includes the plurality of strain sensorpairs on the first beam part on the first axis and the second axis, sothat the third sensor group includes two bridge circuits.
 7. The forcesensor according to claim 3, wherein the sixth sensor group includes theplurality of strain sensor pairs on both the first beam part provided onthe first axis and the first beam part provided on the second axis, sothat the six sensor group includes two bridge circuits.
 8. The forcesensor according to claim 1, wherein the first beam part extends fromthe first structure along the first axis or the second axis.
 9. Theforce sensor according to claim 1, wherein the first beam part extendsfrom the second structure along the first axis or the second axis.